Cyclone separators (“cyclones”) comprise well known means for separating gases and solids from mixtures of the same. Cyclones generally are constructed of a tubular or cylindrical-shaped main body connected to a lower tapered conical portion. A tangential side inlet is provided near the top of the cylindrical main body. A gas outlet tube is provided and generally extends downwardly through the cyclone top into the main body of the cyclone. The tube usually must extend down to a level slightly below the lowest portion of the inlet to assure separation of solids and gases.
In operation, solids-laden gases are introduced at high velocity through the tangential inlet. The solids, which are heavier than the gases, are thrown against the walls of the cyclone by centrifugal force. Gravity then causes the solids to fall toward the bottom of the cyclone. The separated gas follows a vortex path upwardly and passes out of the top of the cyclone through a gas outlet. The gas stream passing out of the top of the cyclone is commonly referred to as the gas overflow. The separated solids exit the cyclone through a solids outlet (also commonly referred to as a discharge outlet) at the base of the tapered conical section. These separated solids are typically referred to as cyclone dust, waste solids, or the discharge underflow.
One example where cyclones are used to separate gas from a gas/solid mixture is in the production of titanium dioxide (“TiO2”). The chloride method for producing TiO2 involves first producing titanium tetrachloride (“TiCl4”) via the chlorination of titanium values in a titanium-containing starting material and then reacting the TiCl4 with oxygen to produce a gas/solid mixture comprising chlorine gas and particulate TiO2. Typically, the TiO2 product is recovered from the gas/solid mixture using a cyclone and the gas is typically recycled back into the process and used to chlorinate additional titanium-containing values in the titanium-containing starting material to produce TiCl4.
The separation of gas from a gas/solid mixture by a cyclone is not 100 percent efficient. Generally, the gas exiting through the gas outlet will carry some solids with it and the solids exiting the cyclone through the solids outlet will be accompanied by some gas as well. The solids exiting the cyclone through the gas outlet are typically filtered out by mechanical means. Typically, the gas exiting the cyclone through the solids outlet must be allowed to escape from the solids or, if that is not an acceptable solution, a means of scrubbing or neutralizing the gas must be employed. If the gas is the desired product, then gas exiting the cyclone through the solids outlet represents an undesirable yield loss in the process. If the gas is intended to be recycled from the gas outlet to the particular process giving rise to the gas/solids mixture (as is the case with chlorine gas in the chloride method described above for producing TiO2), then gas exiting the cyclone through the solids outlet must be replaced as it is lost.